An ancient skeleton from an underwater Mexican cave sheds light on early Americans

Nearly 10,000 years ago, the body of a young woman ended up in a dry cave in southern Mexico. Her bones, discovered by divers in the now-submerged cave, are revealing clues to a short, hard life as well as the history of the first

Americans.

Traditionally, scientists thought just one group of humans crossed a land bridge connecting Asia to North America around 12,000 years ago. But sinkhole caves in the Yucatán Peninsula have yielded nine other skeletons, including a teenage girl linked to modern native Americans (SN: 5/15/14), that suggest humans had already reached that far south by roughly 12,000 years ago.

Explorers mapping a Yucatán cave called Chan Hol found this new female skeleton, dubbed Chan Hol 3, in 2016. Salty cave water degrades collagen in bones, stymieing usual radiocarbon dating methods. But low levels of uranium and thorium in calcite mineral deposits from stalactites that dripped onto Chan Hol 3’s fingers pegged her skeleton to at least 9,900 years old, researchers report February 5 in PLOS ONE.

Tooth cavities indicate she lived on a highsugar diet until she died around age 30. While it’s unclear what killed her, over the years, she sustained three skull injuries — all show healing — and suffered from a bacterial infection.

Comparing Chan Hol 3’s skull to those from Mexico in the same time period revealed two distinct patterns: round skulls with low foreheads in the Yucatán, like Chan Hol 3’s, and longer skulls in Central Mexico. That suggests two human groups — probably with different looks and cultures — coexisted in Mexico around 12,000 to 8,000 years ago, say geoarchaeologist Silvia Gonzalez of the Liverpool John Moores University in England and her colleagues.

Genetic studies could determine whether the two groups had different geographic origins or represent members of the same group that split in Mexico and quickly adapted to their varied environments, she says.